INSECTA. 



163 



The gizzard is adapted for crushing the food, and often has plates 

 or teeth of chitine developed in its walls. It is succeeded by the 

 true digestive cavity (d), which is termed the " the chylific stomach." 

 From this there proceeds an intestine (/), of variable length, which 

 usually terminates in a chamber called the " cloaca " (ff), into which 

 the ducts of the reproductive organs open. The commencement of 

 the gullet is furnished with glandular appendages, which discharge 



Fig. 110. — Digestive apparatus of a Beetle (Carahvs auratiis). a Gullet; 6 Crop; 

 c Gizzard ; d Chylific stomach ; e Malpighian tubes ; / Intestine ; g Cloaca ; A 

 Anal glands. 



the functions of salivary glands. Immediately behind the posterior 

 aperture of the stomach are a variable number of c»cal convoluted 

 tubes (e), which are known as the " Malpighian vessels," after their 

 discoverer Malpighi, and which correspond with the kidneys of 

 higher animals. 



The circulation in insects is mainly carried on by a long con- 

 tractile tube placed along the back, and termed the "dorsal vessel." 

 The blood collected from the various tissues and organs of the body, 

 enters the dorsal vessel from behind, and is driven forwards to the 

 anterior extremity of the body. Eespiration is effected by means of 



